The present invention relates to a sliding member as used for machinery, structures, etc. and more particularly to a sliding member which can be used over a wide range of temperature from room to high temperatures and is suitable to be used in such technical fields wherein lubricants such as oil and grease are difficult to be applied to the sliding surface or when there is some aversion to the use of those lubricants, i.e. a member which is appropriate to be used in so-called dry frictional conditions.
Here throughout the specification and claims the term "sliding member" is intended to represent sliding plates, bushes, bearings, etc. which are used in machinery, apparatuses, structures, etc. which are subject to both load and slide, and also to include seals such as contact type packings which require a sealing function in addition to the above functions.
As sliding members of this kind those lubricants have been publicly known as listed below:
(i) one in which a base metal comprising cast iron, copper alloy, or stainless steel casting is formed with holes or grooves in which solid lubricants such as graphite, molybdenum disulfide, polytetrafluoroethylene (PTFE) or the like are filled and retained therein; PA0 (ii) one in which metal powders of copper alloy, ferrous alloy, etc. are mixed with powders of solid lubricants such as graphite, molybdenum disulfide, and the mixture then being sintered; and PA0 (iii) mixed fabrics of PTFE yarns and other yarns are bonded on a metal material or synthetic resin as a base body by an adhesive or incorporated together by any suitable means.
Although those known sliding members are all superior in heat resistance, they have problems in friction and wear under dry frictional conditions, and also in mechanical strength, in particular the impact strength, and conformability with the mating material is not necessarily good, unable to fulfill its function sufficiently for minute sliding.
In order to solve these problems, as disclosed in U.S. Pat. No. 3,404,061 or Japanese Patent Publication No. 23966/1969 the manufacture of a sliding member by shaping expanded graphite which is obtainable by a special treatment of graphite together with a reinforcing material has been developed. This sliding member has heat resistance, having good conformability to a mating material, and the impact strength is remarkably improved compared with regular graphite, but the coefficient of friction is rather higher than that of regular graphite, and additionally it also has such a defect that it often generates abnormal frictional noises when sliding under dry frictional conditions. Although such sliding members that are obtainable by similarly shaping heat resistant materials such as mica, asbestos, etc. together with a reinforcing material have also been publicly known they also have similar problems.
These problems are considered to be due to a large difference between the coefficients of static and dynamic friction in these heat resistant materials and some flexibility of the sliding member composed of those material, etc. and also the effects of the shapes of the respective elements constituting the sliding system as well as the natural vibrations of the materials thereof.
In order to solve the above problems one of the present inventors already proposed together with several coinventors a sliding member as Japanese Patent Application No. 120701/1981 (hereinafter referred to as "prior art"). Here a brief explanation of the prior art will be given below. That is, it is a sliding member wherein a heat resistant material which is obtainable by mixing one or more of expanded graphite, mica, asbestos, etc. is shaped together with a reinforcing material which comprises a mesh made by weaving or knitting metal filaments, metal fine wires or the like, thus resulting in a sliding member base material, and the surface of the base material is covered with a lubricating compound comprising a polytetrafluoroethylene (PTFE) or tetrafluoroethylene-hexafluoropropylene-copolymer.
However, in this prior art, the lubricating compound covering the surface of the sliding member base material revealed such excellent characteristics that it exhibited low frictional properties in frictional sliding relative to the mating material, in particular in the beginning stage of friction, and low frictional resistance against sliding, generating no abnormal frictional noises. However, even though it exhibited very good characteristics problems have been found in that at higher temperatures a softening flow of the lubricating compound occurs and the compound falls out from the surface, resulting in frictional movement on the heat resistant material of the sliding member base material, and so generating abnormal frictional noises.